Terminal, base station, and communication method for reference signals with phase shift indexes

1. A terminal comprising: circuitry, which, in operation, specifies a frequency domain among a plurality of frequency domains to be used for transmitting a reference signal using predetermined sequence data, determines a phase shift index by adding a phase shift offset value to a phase shift index associated with the specified frequency domain, and applies the determined phase shift index to the reference signal, wherein each of the plurality of frequency domains is associated with a respective phase shift index; and a transmitter, which, in operation, transmits the reference signal to which the determined phase shift index is applied by using the specified frequency domain.

2. The terminal according to claim 1 , wherein a random phase shift index is associated with each of the plurality of frequency domains.

3. The terminal according to claim 2 , wherein the random phase shift index is an index calculated based on a predetermined pseudorandom number.

4. The terminal according to claim 1 , wherein a phase shift index is associated with each of a plurality of continuous frequency domains, and the phase shift indexes associated with the plurality of continuous frequency domains are different from each other.

5. The terminal according to claim 1 , wherein the circuitry, in operation, determines the phase shift offset value based on an ID of the terminal.

6. The terminal according to claim 1 , further comprising: a receiver, which, in operation, receives the phase shift offset value from a base station, wherein the base station transmits different phase shift offset values to terminals.

7. A base station comprising: a receiver, which, in operation, receives a reference signal using predetermined sequence data in a specified frequency domain among a plurality of frequency domains, wherein each of the plurality of frequency domains is associated with a respective phase shift index; and circuitry, which, in operation, generates a base signal, compares the base signal and the reference signal with each other, and estimates a quality of an uplink channel based on the comparison of the base signal and the reference signal with each other, wherein the base signal is generated by determining a phase shift index by adding a phase shift offset value to a phase shift index associated with the specified frequency domain, and applying the determined phase shift index to the reference signal.

8. A communication method comprising: specifying a frequency domain among a plurality of frequency domains to be used for transmitting a reference signal using predetermined sequence data, wherein each of the plurality of frequency domains is associated with a respective phase shift index; determining a phase shift index by adding a phase shift offset value to a phase shift index associated with the specified frequency domain; applying the determined phase shift index to the reference signal; and transmitting the reference signal to which the determined phase shift index is applied by using the specified frequency domain.

9. A communication method comprising: receiving a reference signal using predetermined sequence data in a specified frequency domain among a plurality of frequency domains, wherein each of the plurality of frequency domains is associated with a respective phase shift index; generating a base signal by determining a phase shift index by adding a phase shift offset value to a phase shift index associated with the specified frequency domain, and applying the determined phase shift index to the reference signal; comparing the base signal and the reference signal with each other; and estimating a quality of an uplink channel based on the comparing of the base signal and the reference signal with each other.